Pneumatic and hydraulic cylinders are commonly used in a variety of applications. In laser and optical systems, it is often important to open and block the optical transmission path remotely on command. For this purpose pneumatic or hydraulic cylinders are frequently used to actuate an optical shutter mechanism. Generally a shutter blocks the laser output beam or optical transmission path unless it is deliberately removed from the beam or path. Often the shutter incorporates a mirror surface disposed at an angle with respect to the beam, such that the blocked beam is deflected from its normal path into an optical absorber or "beam dump."
Commonly the shutter is rigidly mounted to a mechanical stage that slides on a rail disposed at substantially a right angle to the beam path. Actuation of the shutter is effected by the extension and retraction of a piston rod attached to the mechanical stage and driven by pressurized gas or hydraulic fluid in a pneumatic or hydraulic cylinder. A piston connected to a piston rod is slidably mounted internal to the cylinder. A system of valves admits pressurized hydraulic fluid or compressed gas, for example air, into the cyinder on one side of the piston, whereupon the piston and connected rod translate axially under the force created by the pressure differential across the cylinder. Depending on which side of the piston is pressurized, the rod either extends or retracts until it reaches the limit of its travel, typically controlled by stops internal to the cylinder. The direction of motion reverses when the pressure differential reverses under control of the valves, or when the pressure is released through a valve and the piston motion is reversed under spring tension. When the rod is extended, the beam path is blocked; when the rod is retracted, the beam path is open. For safety reasons the cylinder is generally configured so that the rod is normally extended, and thus the optical path is blocked, if the cylinder is not pressurized.
Alignment of the piston rod axis with the slide rails for the shutter stage can be critical. Unless these are parallel, the mechanism may bind mechanically. This can result in friction, uneven travel of the shutter stage, chatter and vibration, improper positioning of the shutter, jamming of the shutter mechanism, or damage to the sliding stage, rod, or cylinder. Cylinders are generally mounted rigidly to a system base plate or housing. FIG. 1 illustrates an example of this prior art method. Small offsets or angular misalignments between the cylinder axis and the slide rails can lead to catastrophic shutter failure.
Achieving the required alignment upon assembly and installation of a shutter is typically a highly sensitive, skill-intensive, and time-consuming operation, involving successive minute adjustments of the mechanical components interspersed with sequential loosenings and tightenings of the associated fasteners. It would be highly desirable to have a cylinder mount that could accommodate small to moderate offsets and angular misalignments of the cylinder axis, allowing the latter to conform automatically to the slide rail axis.
Misalignment solutions typically take the form of couplers, generally attached to the end of the rod distal to the cylinder, that offer latitude in tilt, offset, or both. One version uses an elastomeric coupler that flexes. Although it may isolate shock somewhat, it can also fail, causing the rod to become separated from the load. None of these flexible couplers facilitates freedom of rotational orientation, and the additional length of the coupler cannot always be tolerated. Examples are DMA-series cylinder rod couplers manufactured by the Mead company of Chicago, Ill.; cylinder rod couplers manufactured by Compact Air Products, Inc., of Westminster, S.C. (Bulletin #CRC); and NJ-series cylinder rod couplers manufactured by SMC Pneumatics, Inc., of Indianapolis, Ind.
It would also be desirable to have a cylinder mount that could provide cushioning of mechanical shocks that occur at the ends of the piston stroke. Inadequately damped mechanical shock can produce excess noise, vibration of the mechanical and optical assemblies, and wear or early failure of components.
Shock management can be handled a number of ways, but usually by isolation or absorption. Hydraulic or pneumatic dampeners absorb the shock, converting the energy to heat. These shock absorbers are mounted so that the load contacts a piston rod just before the end of a stroke. This slows the load before it strikes a solid stop. These dampeners are effective, but they are expensive and require extra space. A more common method is to place resilient bumpers on the piston inside the cylinder. This does an adequate job and adds little to space, but it does not facilitate alignment or rotation at all. Examples are CF-series, CR-series, and CB-series cushions manufactured by the Mead company of Chicago, Ill.; and NCG-series and NCJ-series cylinders manufactured by SMC Pneumatics, Inc., of Indianapolis, Ind.
An additional desirable feature would be the ability to mount the cylinder at any rotational orientation about its own axis. This would provide flexibility for convenient access to any fittings located on the side wall of the cylinder.
Rotational orientation of the fitting is possible with two types of mount. The main body of the cylinder can be clamped in a squeeze block that, in turn, is mounted to a system support member. Prior to tightening the clamping fasteners, the cylinder can be rotated at will about the piston rod axis. A threaded-nose cylinder protruding through a bracket can be oriented as needed before tightening a nut on the other side of the bracket, although this is limited to situations that allow access to the nut. Neither type allows for misalignment or shock isolation. Examples are 12000-series cylinder-mounting squeeze blocks and 15000-series foot mounting brackets manufactured by Clippard Instrument Laboratory of Cincinnati, Ohio.
Another shortcoming of existing cylinder mounts is the difficulty of threading the piston rod into a load or other object. Existing versions require an estimate of when to engage the cylinder nose threads in order to achieve the proper tightened depth of the threaded rod. Alternatively a tool must be used to grip and twist the rod to achieve proper depth. This may be difficult to access and vulnerable to scratching the rod surface, which is polished to form a sliding seal with the nose of the cylinder.
Compactness would be an attractive feature of any improved cylinder mounting solution. Space is typically at a premium in any laser or optical system. In particular, compactness is important if the improved mount is to be retrofitted into an existing system or design, where dimensional constraints are generally already fixed.
Accordingly, there is a need for a hydraulic or pneumatic cylinder mount that is simultaneously self-aligning, shock-isolating, insensitive to rotational orientation, and compact. There is no known device that provides all of these features and only one known device that provides two features out of the four. All known devices that correct for misalignment add to the overall length of an assembly, thus requiring redesign and making retrofitting difficult or impossible.